#define OE 3
// PGM is also WE# according to data sheet
#define PGM 2

// 18 pin address line
#define Addr0 22
#define Addr18 40

// 8 pin data line
#define Data0 44
#define Data7 51

void setCtrlPins() {
  pinMode(OE, OUTPUT);
  pinMode(PGM, OUTPUT);
}

void setAddrPinsOut() {
  for(int a = Addr0; a <= Addr18; a++) {
    pinMode(a, OUTPUT);
    digitalWrite(a, LOW);
  }
}

void setDataPinsOut() {
  for(int d = Data0; d <= Data7; d++) {
    pinMode(d, OUTPUT);
    digitalWrite(Data0 + d, LOW);
  }
}

void setDataPinsIn() {
  for(int d = Data0; d <= Data7; d++) {
    pinMode(Data0 + d, INPUT);
  }
}

void setByte(byte out) {
  for(int i = 0; i < 8; i++) {
    digitalWrite(Data0 + i, bitRead(out,i));
  }
}

void setAddress(unsigned long addr) {
  for(int i = 0; i < 19; i++) {
    digitalWrite(Addr0 + i, bitRead(addr, i) );
  }
}

byte readByte() {
  byte temp_in = 0;
  for(int i = 0; i < 8; i++) {
    if(digitalRead(Data0 + i)) {
      bitSet(temp_in, i);
    }
  }

  return temp_in;
}

byte readData(unsigned long address) {
  byte temp_read;
  setDataPinsIn();

  digitalWrite(PGM, HIGH);
  digitalWrite(OE, HIGH);

  setAddress(address);

  digitalWrite(OE, LOW);
  delayMicroseconds(1);

  temp_read = readByte();

  return temp_read;
}

void writeByte(byte data, unsigned long address) {
  setAddress(address);
  setByte(data);

  digitalWrite(OE, HIGH);
  digitalWrite(PGM, HIGH);

  delayMicroseconds(2);

  digitalWrite(PGM, LOW);
  delayMicroseconds(1);
  digitalWrite(PGM, HIGH);
}

void programData(byte data, unsigned long address) {
  setDataPinsOut();

  writeByte(0xAA, 0x5555);
  writeByte(0x55, 0x2AAA);
  writeByte(0xA0, 0x5555);
  writeByte(data, address);

  delayMicroseconds(30);

  Serial.println(data, HEX);
  Serial.println(address, HEX);
}

void setup() {
  // Debug trigger
  pinMode(10, OUTPUT);
  digitalWrite(10, LOW);
  // put your setup code here, to run once:
  setCtrlPins();

  setAddrPinsOut();
  setDataPinsOut();

  Serial.begin(9600);
  delay(2);
  Serial.println("Started Serial COM.");
}

void loop() {
  // put your main code here, to run repeatedly:
  programData(0x3F, 0x0000);

  byte data = readData(0x0000);
  // Serial.print("data: ");
  Serial.print("Data returned: ");
  Serial.println(data, HEX);
  // Serial.println("\n");
  delay(1);
}